All Civilizations throughout the history of time have had a sex industry. Empires have risen, and all of them have had a prostitution and drugs underworld tagged to them. Pornography is the next evolutionary step for that element that the human race has craved - since the dawn of time.

The word derives from the Greek πορνογραφία (pornographia), which derives from the Greek words πόρνη (pornē, "prostitute" and pornea, "prostitution"), and γράφω (graphō, "I write or record," derived meaning "illustration," cf. "graph"), and the suffix -ία (-ia, meaning "state of," "property of," or "place of"), thus meaning "a written description or illustration of prostitutes or prostitution."
Because unlike today, thrills were few and far between. Sex was the most thrilling thing that could happen to you in your life for many people. Wanting to hang on to that memory, I think some one made a rock painting or fashioned a bit of clay to relive the moment. Profit motive came, I am sure, shortly after some body else saw and liked the sculpture or painting.